1. Field of the Invention
The present invention relates to an ink composition favorably used for inkjet recording, an inkjet recording method, and a printed material produced therewith.
2. Description of the Related Art
There are various image-recording methods for forming an image on a recording medium such as paper based on an image data signal, including electrophotographic methods, sublimation process or melting process thermal transfer methods, inkjet methods, and the like. An electrophotographic method requires a process for forming an electrostatic latent image on a photoreceptor drum through electrification and exposure, and is problematic since, for example, it requires a complex system, resulting in high production costs. In a thermal transfer method, although the apparatus is inexpensive, there are problems such as high running costs and generation of waste material since an ink ribbon is used. In contrast, an inkjet method employs an inexpensive apparatus, and ink is ejected only to required image portions to directly form an image on a recording medium. Therefore, it is possible to effectively use the ink, thereby reducing running costs. Further, an inkjet method is less noisy. Accordingly, an inkjet method is an excellent image recording method.
In the case of inks for inkjet recording that are curable by the irradiation of radiation such as ultraviolet rays (radiation-curable type ink for inkjet recording), it is necessary to provide sufficiently high sensitivity and high image quality. High sensitivity provides the ink with high curability with respect to radiation, resulting in many advantages such as reduced electric power consumption, elongation of service life due to diminished load on a radiation generator, and prevention of the generation of low molecular weight materials caused by insufficient curing.
Ultraviolet ray-curable type inkjet methods have come under scrutiny in recent years due to the advantages of relatively low odor generation, quick drying property, and the possibility of recording on a recording medium having no ink absorption property. In particular, benzyl, benzoin, benzoin ethyl ether, Michler's ketone, anthraquinone, acridine, phenazine, benzophenone, 2-ethylanthraquinone or the like have been generally used as a photopolymerization initiator, (see, for example, Bruce M. Monroe et. al., Chemical Reviews, Vol. 93, (1993), pp. 435-448). However, when such photopolymerization initiators are used, since the curing sensitivity of a photopolymerizable composition is low, a long period of time is required for the image exposure in image formation. Consequently, if slight shaking exists in the operation, for fine images, an image having good image quality cannot be reproduced and, further, since the energy emission amount of a light source for the exposure must be increased, the irradiation of a large amount of generated heat associated therewith must be taken into consideration.
JP-A No. 2006-182970 proposes an ink composition for inkjet recording and the ink composition of JP-A. 2006-182970 contains a polymerizable compound, a colorant, and a hydrophobic polymer such as a fluorine group-containing polymer, for the purpose of providing an ink for inkjet recording that has high curing sensitivity and provides an image having favorable image quality. However, the ink composition for inkjet recording as described in the JP-A No. 2006-182970 is problematic in that the viscosity is high because the ink contains a polymer component.